Temperatures in these mountains—which include the Western Alps, Pyrenees, and Massif Central—crossed a threshold around 1985, the researchers say.

Before that year the region shows no clear trend in climate changes. But since then the mountains have been warming, and plants began moving in sync with rising temperatures.

The scientists looked at the movements of 171 species in forests on the lower slopes, from sea level up to 8,500 feet (2,600 meters).

While earlier studies had focused on plants in high altitudes that are known to be more sensitive to temperature changes, the new work found that even common plants at lower elevations are feeling the heat.

The team also discovered that different types of plants are moving at different rates.

"Long-lived plants like trees or shrubs did not show a significant shift, whereas short-lived species like herbs showed a strong upward shift in elevation," Lenoir said.

"This may imply profound changes in the composition and the structure of plant communities and on the animal species they interact with," he added. "It may disrupt ecosystems."

Out of Room

Steven Running is an ecologist at the University of Montana in Missoula who was not involved in the new study.

"Theory would predict that warming temperatures will allow plant distributions to expand into cooler, higher mountain elevations," he said.

"This paper confirms the theory. With a large population analysis, [it is] the best evidence published so far that plant distributions are rising [in altitude]."

The shifts in elevations of some plants and not others "shows very much that the ecosystems are already evolving away from the ecosystems as we know them," added Cynthia Rosenzweig of the NASA Goddard Institute for Space Studies in New York City.